The invention relates to cryogenic apparatus for surgery with a closed cooling circuit comprising a holder of the surgical instrument provided with an applicator with a porous heat exchanger composed of metal grids or of sintered metal, advantageously of silver or copper, a storage vessel for liquid gas in a handle and a regulating unit.
Cryogenic surgical systems, frequently also called cryocauters, have been recently more widely used in surgery of tumorous diseases, where for cooling of a warm instrument applied to the place to be surgically treated either the expansion of some compressed gases, for instance carbon dioxide CO.sub.2 or nitrogen oxide N.sub.2 O or on internal circulation of liquefied gases, mostly nitrogen are used.
Systems with expansion cooling operate usually with an overpressure about 5 MPa, which must be also present in the surgical instrument itself which is relatively dangerous. Systems with cooling by a cyrogenic liquid are usually designed to operate either by gravity, where the liquid nitrogen flows from a storage vessel of the cryocauter, where it has been prior poured in an estimated amount through an insulated tube to the surgical instrument which it cools and is discharged in gaseous condition through another tube, or they operate at a pressure about 0.5 MPa, where liquid medium is supplied from an external storage vessel to the surgical instrument, where it turns into gas and is removed through a system of connecting tubes back to the storage vessel, where it is discharged into the atmosphere.
Systems operating by gravity have serious drawbacks in a very slow cooling and the impossibility of adjustment of the extent of cooling otherwise than by the variation of the amount of the cooling liquid filled into the storage vessel. Another limitation is the necessity to maintain a predetermined position of the surgical instrument in order to prevent spilling of the cryogenic liquid but of the storage vessel in the course of the surgical treatment.
Pressure systems provided with an external storage vessel for the cryogenic liquid enable dosing of the cooling effect and in some cases also the adjustment of the temperature, but they involve the risk connected with the high overpressure of about 0.5 MPa in the thin-walled surgical instrument. In addition the long connecting supply tube for liquid nitrogen is at the start of the surgery cooled for a relatively long time, the cooling of the instrument in contact with the tissue to a temperature below -150.degree. C. lasts even several minutes; this leads in case of surgery of tumorous diseases to a low efficiency of necrotization of tumorous cells.